The present invention relates to bearing plates for use in the support of mine roofs, and the like.
In mine work, such as coal mining, or in underground formations such as tunnels or excavations, it is necessary to reinforce or support the roof and/or walls of the excavation to prevent rock falls or cave-ins. The most common means presently in use for effecting such support include elongated bolts or rods which are anchored in blind drill holes to hold a metal support plate in close contact with the roof or wall surface surrounding the hole. The vast majority of support plates have a central opening through which the bolt or rod passes. An integral head or threaded nut on the bolt or bar engages the plate in the area surrounding the central opening, sometimes with a hardened washer therebetween. In many installations the bolts are tensioned to several thousand pounds after being anchored at the end within the drill hole, this force being transferred to the support plate to exert a compressive force on the rock formation.
In order to provide the support and reinforcement function with the necessary degree of safety, the plates must meet certain levels of strength and rigidity, as well as being installed at appropriate intervals about the mine roof or walls. Governmental agencies have been established to set standards and supervise compliance therewith in order to insure that mine safety standards are being met. These standards require submission to and approval by the agency of a specific "roof plan" for every underground mine, setting forth the type and location of each support, as well as the individual elements used in providing the support and reinforcement. As applied to roof support plates, for example, the standards require that the plates deflect not more than a specified maximum under designated load conditions.
For reasons of both economy and ease of handling and installation, it is desirable that the support plates be as small, thin and lightweight as possible while still meeting the required standards. Economies may also be achieved by keeping the tooling and operations used in fabricating the plates as simple and inexpensive as possible. While plates of flat sheet metal, normally steel, simply cut to the proper external dimensions and punched at the center will meet the standards if thick enough, it has been found that additional structural rigidity may be imparted by embossing the plates with a suitable die. Therefore, the thickness, and accordingly the weight and cost of the material, has been reduced from that of flat plates by embossing the plate in various ways. In general, the prior art plates have been embossed in an annular pattern which encircles the central opening and/or the opening is included in the embossed area.
Embossed roof plates currently in commercial use include those generally referred to as "bell-type" and "donut-type" plates. Also, various forms of roof plates and support systems are shown and described in U.S. Pat. Nos. 3,163,012 of Dempsey, 3,161,174 of Harrison, 3,238,731 of Seifert, et al, 3,415,064 of Talobre, 3,478,523 of Reusser, et al, 3,090,203 of Durget and 4,037,418, 4,095,430 and 4,095,431, the latter three all of Hannan, and French Pat. Nos. 1,222,640 and 1,304,298.